EP3390097B1 - Tyre having improved wear and rolling resistance properties - Google Patents

Description

The present invention relates to a tire with a radial carcass reinforcement and more particularly to a tire intended for fitting vehicles carrying heavy loads and traveling at sustained speed, such as, for example, trucks, tractors, trailers or road buses.

In general, in heavy-duty type tires, the carcass reinforcement is anchored on both sides in the bead zone and is surmounted radially by a crown reinforcement made up of at least two superimposed layers. and formed of parallel wires or cables in each layer and crossed from one layer to the next making angles of between 10 ° and 45 ° with the circumferential direction. Said working layers, forming the working reinforcement, may also be covered with at least one so-called protective layer and formed from advantageously metallic and extensible reinforcing elements, called elastic. It may also comprise a layer of low extensibility metal wires or cables forming an angle of between 45 ° and 90 ° with the circumferential direction, this ply, called triangulation ply, being located radially between the carcass reinforcement and the first ply of so-called working top, formed of parallel wires or cables having angles at most equal to 45 ° in absolute value. The triangulation ply forms with at least said working ply a triangulated reinforcement, which presents, under the various stresses to which it is subjected, little deformation, the triangulation ply having the essential role of taking up the transverse compressive forces of which is the 'object all the reinforcement elements in the region of the crown of the tire.

Cables are said to be inextensible when said cables have, under a tensile force equal to 10% of the breaking force, a relative elongation at most equal to 0.2%.

Cables are said to be elastic when said cables have, under a tensile force equal to the breaking load, a relative elongation at least equal to 3% with a maximum tangent modulus of less than 150 GPa.

Circumferential reinforcing elements are reinforcing elements which form angles with the circumferential direction in the range + 2.5 °, - 2.5 ° around 0 °.

The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.

The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.

The radial direction is a direction intersecting the axis of rotation of the tire and perpendicular to the latter.

The axis of rotation of the tire is the axis around which it rotates in normal use.

A radial or meridian plane is a plane which contains the axis of rotation of the tire.

The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.

With regard to metal wires or cables, the measurements of force at break (maximum load in N), resistance at break (in MPa), elongation at break (total elongation in%) and modulus ( in GPa) are carried out in tension according to the ISO 6892 standard of 1984.

As regards the rubber compositions, the modulus measurements are carried out in tension according to the AFNOR-NFT-46002 standard of September 1988: the nominal secant modulus (or, after an accommodation cycle) is measured in second elongation (ie, after an accommodation cycle). apparent stress, in MPa) at 10% elongation (normal temperature and humidity conditions according to the AFNOR-NFT-40101 standard of December 1979).

Certain current tires, known as “road” tires, are intended to run at high speed and on increasingly long journeys, due to the improvement of the road network and the growth of the motorway network in the world. The set of conditions under which such a tire is called upon to run undoubtedly allows an increase in the number of kilometers traveled, the wear of the tire being less; on the other hand, the endurance of the latter and in particular of the crown reinforcement is penalized.

There are indeed stresses at the level of the crown reinforcement and more particularly shear stresses between the crown layers, combined with a not insignificant rise in the operating temperature at the level of the ends of the axially most crown layer. short, which results in the appearance and propagation of cracks in the rubber at said ends.

In order to improve the endurance of the crown reinforcement of the type of tire studied, solutions relating to the structure and quality of the layers and / or profiles of rubber compounds which are arranged between and / or around the ends of plies and more particularly the ends of the axially shorter ply have already been made.

It is in particular known to introduce a layer of rubber mixture between the ends of the working layers to create a decoupling between said ends to limit the shear stresses. However, such decoupling layers must have very good cohesion. Such layers of rubber mixtures are for example described in the patent application WO 2004/076204 .

The tires thus produced effectively make it possible to improve performance, in particular in terms of endurance.

Furthermore, it is known to produce tires with a very wide tread or else to give tires of a given dimension greater load capacities to introduce a layer of circumferential reinforcing elements. The patent application WO 99/24269 describes for example the presence of such a layer of circumferential reinforcing elements.

The layer of circumferential reinforcing elements is usually formed by at least one metallic cable wound to form a turn, the laying angle of which with respect to the circumferential direction is less than 2.5 °.

The document WO 2013/083339 further describes a tire comprising a layer of circumferential reinforcing elements associated with calendering mixtures of the working layers conferring improved rolling resistance properties.

In combination with this internal tire structure, it is known to provide the tread, that is to say the part of the tire intended to come into contact with the ground during rolling and to wear out during rolling, of a sculpture formed of elements in relief delimited by grooves whether they are of circumferential, transverse or oblique orientation. The objective of such a tread is to give the tread good performance when rolling on dry pavement and on pavement coated with water, in particular in rainy weather.

To improve the performance of treads without, however, reducing the shear stiffness of said bands too much, it is known to form on the tread surface a plurality of ridges oriented transversely or obliquely in order to cut the film of water on a roadway. to ensure good contact between the tread and the road. One means of obtaining such ridges consists in providing the strip with a plurality of cutouts, these cutouts having the form of grooves or the form of incisions. We distinguish, in the present application, the incisions of the grooves in that the incisions have an appropriate width to allow during the rolling at least partial contact between the vis-à-vis walls delimiting these incisions and in particular during the passage through contact with the ground, which cannot be the case for the grooves under normal conditions of tire use.

Combined with this need to improve the grip performance by the presence of ridges formed by the transverse cutouts, it is also required that the performance of a tread be durable, that is to say that the performance of a tread is durable. satisfactory are achieved even after more or less advanced partial wear. By partial wear of a tread is meant a state of wear corresponding to a tread thickness at most equal to the total thickness of the tread which can be worn before having to change the tire, in particular for regulatory reasons. .

The patent application WO 02/38399-A2 describes a tread for a heavy vehicle tire, this tread comprising a plurality of circumferential and transverse grooves. The transverse grooves are formed by alternating recessed areas and incisions so as to have a volume of hollows opening onto the running surface when new and a volume of hidden hollows, these hidden hollows being intended to open after partial wear of the same tread. The presence of hidden hollows - appearing with wear, allows for greater rigidity in the initial state while ensuring a grip performance regardless of the level of wear of the belt.

The documents FR 2 950 565 , WO 2010/0320276 , FR 3 014 022 and WO 2014/102136 , describe for example cutouts with longitudinal orientation and cutouts with transverse orientation.

During tests, the inventors have demonstrated that the presence of the combination of longitudinal and transverse cutouts comprising hidden hollows, the dimension of the hidden hollows possibly being relatively small for the two types of cutouts, could lead to degradation of the cutouts. performance in terms of wear, with the appearance of irregular forms of wear, in comparison with similar tires not comprising such hidden hollows for identical uses.

Furthermore, current requirements guide the design of tires so that they participate in reducing the fuel consumption of vehicles.

An object of the invention is to provide tires whose wear properties and more specifically of wear regularity are preserved or improved whatever the use, the tires comprising a combination of longitudinal and transverse cutouts comprising hidden hollows. present on the tread and whose performance in terms of rolling resistance is improved to contribute to lower fuel consumption by vehicles fitted with such tires.

This object is achieved according to the invention by a tire with radial carcass reinforcement comprising a crown reinforcement formed of at least two working crown layers of reinforcing elements, each formed of inserted reinforcing elements. between two calendering layers of rubber mixture, itself capped radially with a tread, said tread being joined to two beads by means of two sidewalls, the crown reinforcement comprising at least one layer of circumferential reinforcing elements, said tread comprising a tread surface intended to come into contact with a roadway and form a contact surface, said tread band consisting of at least a central part extending at least in the area of the equatorial plane and two axially outer parts and having at least in said central part at least one cutout of longitudinal orientation and at least one cutout of transverse orientation, the depth, measured on a new tire in at least said central part, of said at least one cutout of longitudinal orientation being greater than or equal to 40% of the thickness of the tread, the ratio of the width geur measured at the bottom of said at least one cutout of longitudinal orientation over the width measured at the surface of the tread on a new tire of said at least one cutout of longitudinal orientation being greater than 1.2, the depth, measured on a new tire in at least said central part, of said at least one transverse orientation cutout being greater than or equal to 40% of the thickness of the tread, the ratio of the width measured at the bottom of said at least one orientation cutout transverse over the width measured at the surface of the tread on a new tire of said at least one transverse orientation cutout being greater than or equal to 1, the modulus of elasticity under tension at 10% elongation of at least one calendering layer of at least one working crown layer being greater than 9 MPa and the maximum value of tan (δ), denoted tan (δ) _max , of said at least one calendering layer of at least one neck che of working peak being less than 0.100.

Within the meaning of the invention, a cutout generically designates either a groove or an incision and corresponds to the space delimited by walls of material facing each other and spaced from each other by a non-zero distance ( known as "cutout width"). What differentiates an incision from a groove is precisely this distance; in the case of an incision, this distance is appropriate to allow at least partial contacting of the opposite walls delimiting said incision at least during the passage in contact with the roadway. In the case of a groove, the walls of this groove cannot come into contact with one another under normal rolling conditions.

For the purposes of the invention, a cutout of longitudinal orientation is a cutout the mean plane of which of at least part of the walls of said cutout forms an angle with a longitudinal plane of less than 10 °. This angle formed with a longitudinal plane can be oriented in one direction or the other with respect to said longitudinal plane. A cutout of longitudinal orientation can also be a cutout whose walls undulate or zigzag around a mean plane such as has just been described.

For the purposes of the invention, a cutout of transverse orientation is a cutout whose mean plane of at least part of the walls of said cutout forms an angle with a radial plane of less than 35 °. This angle formed with a radial plane can be oriented in one direction or the other with respect to said radial plane. A cutout of transverse orientation can also be a cutout which runs continuously on either side of a mean plane as has just been described; it may also be a cutout, the walls of which undulate or zigzag around a mean plane as has just been described.

For the purposes of the invention, the depth of a cutout is the radial distance measured on a new tire between the surface of the tread and the radially innermost point of said cutout.

For the purposes of the invention, the thickness of the tread, measured in a radial section of the tire, is the distance measured on a new tire between a point on the surface of the tread and the orthogonal projection of said point on the surface. radially outwardly of the crown reinforcement.

The width between the walls of a cutout is measured on a new tire, in a section plane perpendicular to the mean plane of the walls and to the plane tangent to the surface of the tread. It is measured in a direction parallel to the plane tangent to the surface of the tread.

For the purposes of the invention, the width between the walls of a cutout at the surface of the tread corresponds to the smallest measurement in the radially outer part of the cutout and more exactly to the smallest measurement made in a zone lying radially between a radially outermost point of said cutout and a point located at a distance from the surface of the tread equal to 30% of the depth of said cutout.

For the purposes of the invention, a measurement at the bottom of a cutout corresponds to the largest measurement in the radially inner part of the cutout and more exactly to the largest measurement taken in a zone lying radially between the point radially on more inside said cutout and a point located at a distance from the surface of the tread equal to 25% of the depth of said cutout.

According to the invention, the central part of the tread extending at least in the zone of the equatorial plane has an axial width at least as great as that of the layer of circumferential reinforcing elements.

The loss factor tan (δ) is a dynamic property of the rubber compound layer. It is measured on a viscoanalyst (Metravib VA4000), according to standard ASTM D 5992-96. The response of a sample of vulcanized composition (cylindrical test piece 2 mm thick and 78 mm ² in section) is recorded, subjected to a sinusoidal stress in alternating simple shear, at a frequency of 10 Hz, at a temperature of 100 ° C. A strain amplitude sweep is carried out from 0.1 to 50% (outward cycle), then from 50% to 1% (return cycle). The results used are the complex dynamic shear modulus (G *) and the loss factor tan (δ) measured on the return cycle. For the return cycle, we indicate the maximum value of tan (δ) observed, denoted tan (δ) _max .

Rolling resistance is the resistance that appears when the tire is rolling. It is represented by the hysteretic losses linked to the deformation of the tire during one revolution. The frequency values linked to the revolution of the tire correspond to values of tan (δ) measured between 30 and 100 ° C. The value of tan (δ) at 100 ° C thus corresponds to an indicator of the rolling resistance of the tire when rolling.

It is still possible to estimate the rolling resistance by measuring the energy losses by rebound of the samples at imposed energy at temperatures of 60 ° C. and expressed as a percentage.

Advantageously according to the invention, the loss at 60 ° C., denoted P60, of said at least one calendering layer of at least one working crown layer is less than 20%.

According to a preferred embodiment of the invention, the modulus of elasticity under tension at 10% elongation of the calendering layers of said at least two working crown layers is greater than 9 MPa and the value tan (δ) _max calendering layers of said at least two working crown layers is less than 0.100.

The tests carried out have shown that the use of such mixtures whose moduli of elasticity are greater than 9 MPa and whose tan (δ) _{max value} is less than 0.100 makes it possible to improve the properties of the tire in terms of rolling resistance. while retaining satisfactory endurance properties.

More conventional tire designs provide calendering layers of the working crown layers with tensile moduli at 10% elongation substantially equivalent to those of said at least one calendering layer of at least one layer of. working crown according to the invention but maximum values of tan (δ), denoted tan (δ) _max , of the calendering layers of the working crown layers greater than 0.120. Such mixtures, which are more usual for this type of layer, lead to better cohesion.

For the purposes of the invention, a cohesive rubber mixture is a rubber mixture which is particularly resistant to cracking. The cohesion of a mixture is thus evaluated by a fatigue cracking test carried out on a “PS” (pure shear) specimen. It consists in determining, after notching of the test piece, the crack propagation speed “Vp” (nm / cycle) as a function of the energy release rate “E” (J / m ² ). The experimental field covered by the measurement is included in the range -20 ° C and + 150 ° C in temperature, with an atmosphere of air or nitrogen. The stress on the test piece is an imposed dynamic displacement of amplitude between 0.1mm and 10mm in the form of a stress of the pulse type (tangent “haversine” signal) with a rest time equal to the duration of the pulse; the frequency of the signal is of the order of 10 Hz on average.

• Une accommodation de l'éprouvette « PS », de 1000 cycles à 27% de déformation.
• une caractérisation énergétique pour déterminer la loi « E » = f (déformation). Le taux de restitution d'énergie « E » est égal à W0^∗h0, avec W0 = énergie fournie au matériau par cycle et par unité de volume et h0 = hauteur initiale de l'éprouvette. L'exploitation des acquisitions « force / déplacement » donne ainsi la relation entre « E » et l'amplitude de la sollicitation.
• La mesure de fissuration, après entaillage de l'éprouvette « PS ». Les informations recueillies conduisent à déterminer la vitesse de propagation de la fissure « Vp » en fonction du niveau de sollicitation imposé « E ».

The measure consists of 3 parts:

• Accommodation of the "PS" test piece, 1000 cycles at 27% deformation.
• an energetic characterization to determine the law “E” = f (deformation). The rate of energy release “E” is equal to W0 ^∗ h0, with W0 = energy supplied to the material per cycle and per unit of volume and h0 = initial height of the test piece. The exploitation of the acquisitions “force / displacement” thus gives the relation between “E” and the amplitude of the request.
• The cracking measurement, after notching of the “PS” test piece. The information collected leads to determine the speed of propagation of the crack “Vp” according to the level of stress imposed “E”.

The tests carried out have also shown that the tires according to the invention exhibit satisfactory wear performance and in particular wear regularity regardless of the conditions of use of the tires.

The inventors have in fact been able to demonstrate that the combination of cutouts with longitudinal orientation and cutouts with transverse orientation, the depth of which is greater than 40% of the thickness of the tread and the ratio of the width measured to bottom of said longitudinal cutouts over the width measured at the surface of the tread of said cutouts is greater than 1.2 and of which the ratio of the width measured at the bottom of said transverse cutouts to the width measured at the surface of the tread of said cutouts is greater or equal to 1, associated with at least one calendering layer of at least one working crown layer whose modulus of elasticity under tension at 10% elongation is greater than 9 MPa and whose maximum value of tan (δ ), denoted tan (δ) max, is less than 0.100 lead to local deformations of the crown reinforcement during the manufacture of the tire and in particular during the curing of the latter. The inventors intend to interpret this deformation of the crown reinforcement due to creep of uncontrolled elastomeric materials at said cutouts comprising hidden hollows during the molding and curing of said tire. This would probably result in a deformation in the radial direction of the constituent layers of the crown reinforcement located near said cutouts. These deformations could lead, during use of the tires, to an alteration in the performance of the tire in terms of wear and in particular of regularity of wear, the thickness of the mixture to be worn not being regular in the transverse and longitudinal directions of the tire. The additional presence of at least one calendering layer of at least one working crown layer whose modulus of elasticity under tension at 10% elongation is greater than 9 MPa and whose maximum value of tan (δ) , noted tan (δ) max, is less than 0.100 does not seem favorable to better control of the creep of elastomeric materials; on the contrary, the presence of such a calendering layer seems to promote this phenomenon of deformation of the crown reinforcement during the manufacture of the tire and in particular during the curing of the latter.

The inventors have further demonstrated that the hollows hidden within cutouts oriented in the longitudinal direction with relatively small dimensions since they are associated with a series of transverse cutouts not including hidden hollows, which they 'acts of grooves or transverse incisions, also lead to a deformation in the radial direction of the constituent layers of the crown reinforcement.

The presence of the layer of circumferential reinforcing elements in accordance with the invention makes it possible to limit or even prevent these phenomena of irregular wear in the transverse and longitudinal directions of the tire.

The inventors intend to interpret the results obtained with the tires according to the invention by the presence of a layer of circumferential reinforcing elements which seems to be able to reduce or even avoid said local deformations of the crown reinforcement during the curing of tires comprising longitudinal and transverse orientation cutouts the depth of which is greater than or equal to 40% of the thickness of the tread and the ratio of the width measured at the bottom of the longitudinal orientation cutouts to the width measured at the surface of the tread of the longitudinal orientation cutouts is greater than 1.2 and whose ratio of the width measured at the bottom of said transverse cutouts to the width measured at the surface of the tread of said cutouts is greater than or equal to 1, associated with at least one calendering layer of at least one working crown layer of which the modulus of elasticity under tension at 10% elongation is greater than 9 MPa and the maximum value of tan (δ), denoted tan (δ) max, is less than 0.100.

Very surprisingly, the layer of circumferential reinforcing elements, which is usually present to limit the effects of shearing between the working crown layers, seems to allow better control of the movements of the mixtures forming the tread during the curing of the tread. 'a tire, the latter comprising cutouts of longitudinal orientation comprising hidden hollows and cutouts of transverse orientation including or not comprising hidden hollows, associated with at least one calendering layer of at least one working crown layer whose modulus of elasticity under tension at 10% elongation is greater than 9 MPa and whose maximum value of tan (δ), denoted tan (δ) max, is less than 0.100.

Furthermore, the inventors have been able to demonstrate that the layer of circumferential reinforcing element allows choices of rubber mixtures of the calendering layers of the working crown layers exhibiting less favorable cohesion without adversely affecting the endurance properties of the tire.

The inventors have in particular demonstrated that the presence of at least one layer of circumferential reinforcing elements contributes to less change in the cohesion of the calendering layers of the working crown layers. In fact, the more usual tire designs comprising in particular calendering layers of the working crown layers with values of tan (δ) _max greater than 0.120 lead to a change in the cohesion of said calendering layers of the working crown layers. , this tending to weaken. The inventors observe that the presence of at least one layer of circumferential reinforcing elements which limits the shear stresses between the ends of the working crown layers and, in addition, limits the temperature increases, leads to a weak change in the cohesion. of said calendering layers of the working crown layers. The inventors thus consider that the cohesion of said at least one calendering layer of at least one working crown layer, weaker than what exists in more conventional tire designs, is satisfactory in the design of the tire according to the invention. invention.

The inventors have thus been able to demonstrate that the presence of at least one layer of circumferential reinforcement elements makes it possible to maintain performance, in particular in terms of endurance and in terms of satisfactory wear in the presence of the combination according to the invention. longitudinal oriented cutouts comprising hidden recesses and transversely oriented cutouts whether or not including hidden recesses and a modulus of elasticity under tension at 10% elongation of said at least one calendering layer of at least at least one working crown layer greater than 9 MPa and having a tan (δ) _{max value} of said at least one calendering layer of at least one working crown layer less than 0.100.

According to one embodiment of the invention, the ratio of the width measured at the bottom of said at least one cutout of transverse orientation to the width measured at the surface of the tread on a new tire of said at least one cutout of transverse orientation is strictly greater than 1.2.

According to this embodiment, the transverse orientation cutout preferably has a ratio of the width measured at the bottom of said at least one transverse orientation cutout to the width of said at least one transverse orientation cutout measured at the surface of the tread on a new tire greater than 1.2 over its entire length.

According to a variant of this embodiment, this condition on the ratio of the width measured at the bottom of said at least one cutout of transverse orientation over the width of said at least one cutout of transverse orientation measured at the surface of the strip of New tire bearing greater than 1.2 may only be checked over part of the length of the transverse orientation cutout.

According to yet other variants of this embodiment, this condition on the ratio of the width measured at the bottom of said at least one cutout of transverse orientation over the width of said at least one cutout of transverse orientation measured in surface area of the tread on a new tire greater than 1.2 can be checked intermittently along the length of the transverse orientation cutout.

According to an alternative embodiment of the invention, the width measured at the bottom of said at least one transverse orientation cutout is strictly greater than 2 mm.

Advantageously according to the invention, the width measured at the bottom of said at least one transverse orientation cutout is less than 10 mm.

According to a preferred variant of the invention, the cutout of longitudinal orientation has a ratio of the width measured at the bottom of said at least one cutout of longitudinal orientation to the width of said at least one cutout of longitudinal orientation measured at the surface. of the tread on a new tire greater than 1.2 over its entire length.

According to another variant of the invention, this condition on the ratio of the width measured at the bottom of said at least one cutout of longitudinal orientation over the width of said at least one cutout of longitudinal orientation measured at the surface of the strip of New tire bearing greater than 1.2 may only be checked over part of the length of the longitudinal orientation cutout.

According to yet other variants of the invention, this condition on the ratio of the width measured at the bottom of said at least one cutout of longitudinal orientation over the width of said at least one cutout of longitudinal orientation measured at the surface of the New tire tread greater than 1.2 can be checked intermittently along the length of the longitudinal orientation cutout.

According to another variant embodiment of the invention, the width measured at the bottom of said at least one cutout of longitudinal orientation is strictly greater than 3 mm.

Advantageously according to the invention, the width measured at the bottom of said at least one cutout of longitudinal orientation is less than 10 mm.

Advantageously according to the invention, the volume notch rate of the tread of the tire according to the invention is less than or equal to 15%, preferably less than or equal to 13% and more preferably greater than 5%.

The volume notch rate of the tread is defined according to the invention on a new tire by the ratio of the volume of cutouts to the total volume of the tread. The total volume of the tread is for its part defined in the sense of the invention by the volume, including the volume of all the cutouts, evaluated between the tread surface and a surface parallel to this tread surface passing through the bottom. the innermost recess of the strip.

1. a) soit par du noir de carbone de surface spécifique BET inférieure à 60 m²/g, quelle que soit son indice de structure, employé à un taux compris entre 40 et 100 pce, et de préférence entre 60 et 90 pce,
2. b) soit par une charge blanche de type silice et/ou alumine comportant des fonctions de surface SiOH et/ou AlOH choisie dans le groupe formé par les silices précipitées ou pyrogénées, les alumines ou les aluminosilicates ou bien encore les noirs de carbone modifiés en cours ou après la synthèse de surface spécifique BET comprise entre 30 et 260 m²/g employée à un taux compris entre 40 et 100 pce, et de préférence entre 60 et 90 pce,
3. c) soit par un coupage de noir de carbone décrit en (a) et d'une charge blanche décrite en (b), dans lequel le taux global de charge est compris entre 40 et 100 pce, et de préférence entre 60 et 90 pce.

According to a preferred embodiment of the invention, said at least one calendering layer of at least one working crown layer is an elastomeric blend based on natural rubber or synthetic polyisoprene with a majority of cis-1 chains, 4 and optionally of at least one other diene elastomer, the natural rubber or synthetic polyisoprene, in the event of cutting, being present at a majority rate relative to the rate of the other or of the other diene elastomers used and of a reinforcing filler constituted :

1. a) either by carbon black with a BET specific surface area of less than 60 m ² / g, whatever its structure index, used at a rate of between 40 and 100 phr, and preferably between 60 and 90 phr,
2. b) either by a white filler of silica and / or alumina type comprising SiOH and / or AlOH surface functions chosen from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates or even carbon blacks modified in during or after the synthesis of BET specific surface of between 30 and 260 m ² / g used at a rate of between 40 and 100 phr, and preferably between 60 and 90 phr,
3. c) either by cutting carbon black described in (a) and a white filler described in (b), in which the overall filler rate is between 40 and 100 phr, and preferably between 60 and 90 phr .

The BET specific surface measurement is carried out according to the method of BRUNAUER, EMMET and TELLER described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938 , corresponding to the NFT 45007 standard of November 1987.

In the case of using a clear filler or a white filler, it is necessary to use a coupling and / or covering agent chosen from agents known to those skilled in the art. As examples of preferential coupling agents, mention may be made of sulfurized alkoxysilanes of the bis- (3-trialkoxysilylpropyl) polysulfide type, and among these in particular bis- (3-triethoxysilylpropyl) tetrasulfide sold by the company DEGUSSA under the denominations Si69 for the pure liquid product and X50S for the solid product (50/50 blend by weight with N330 black). As examples of covering agents, mention may be made of a fatty alcohol, an alkylalkoxysilane such as a hexadecyltrimethoxy or triethoxysilane, respectively sold by the company DEGUSSA under the names Si116 and Si216, diphenylguanidine, a polyethylene glycol, a silicone oil optionally modified by means of OH or alkoxy functions. The covering and / or coupling agent is used in a weight ratio with respect to the load ≥ to 1/100 and ≤ to 20/100, and preferably between 2/100 and 15/100 when the clear load represents the all of the reinforcing filler and between 1/100 and 20/100 when the reinforcing filler consists of a cut of carbon black and a light filler.

As other examples of reinforcing fillers having the morphology and the SiOH and / or AlOH surface functions of the materials of silica and / or alumina type described above and which can be used according to the invention as a partial or total replacement thereof, it is possible to cite carbon blacks modified either during the synthesis by adding a silicon and / or aluminum compound to the furnace feed oil or after the synthesis by adding, to an aqueous suspension of carbon black in a solution of sodium silicate and / or aluminate, an acid so as to at least partially cover the surface of the carbon black with SiOH and / or AlOH functions. As non-limiting examples of this type of carbonaceous fillers with SiOH and / or AlOH functions at the surface, mention may be made of the CSDP type fillers described in ACS Meeting Conference N ° 24, Rubber Division, Anaheim, California, May 6-9, 1997 as well as those of the patent application EP-A-0 799 854 .

When a clear filler is used as the only reinforcing filler, the hysteresis and cohesion properties are obtained by using a precipitated or pyrogenic silica, or else a precipitated alumina or even a surface aluminosilicate. specific BET between 30 and 260 m ² / g. As nonlimiting examples of this type of filler, mention may be made of silicas KS404 from the company Akzo, Ultrasil VN2 or VN3 and BV3370GR from the company Degussa, Zeopol 8745 from the company Huber, Zeosil 175MP or Zeosil 1165MP from the company Rhodia, HI -SIL 2000 from PPG, etc ...

Among the diene elastomers which can be used in a blend with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, there may be mentioned a polybutadiene (BR) preferably with a majority of cis-1,4 chains, a styrene-butadiene copolymer (SBR) solution or emulsion, a butadiene-isoprene copolymer (BIR) or even a styrene-butadiene-isoprene terpolymer (SBIR). These elastomers can be elastomers modified during polymerization or after polymerization by means of branching agents such as a divinylbenzene or starring agents such as carbonates, halo tins, halosilicums or even by means of agents of functionalization leading to grafting onto the chain or at the end of the chain of oxygenated carbonyl or carboxyl functions or else of an amine function such as for example by the action of dimethyl or of diethylamino benzophenone. In the case of cuts of natural rubber or synthetic polyisoprene with a majority of cis-1,4 linkages with one or more of the diene elastomers mentioned above, natural rubber or synthetic polyisoprene is preferably used at a majority rate. and more preferably at a rate greater than 70 phr.

The choice of the reinforcing filler intervening in the rubber mixture constituting said at least one calendering layer of at least one working crown layer contributes both to obtaining values of modulus of elasticity under tension at 10% d 'elongation and obtaining the values of tan (δ) _max . However, within the above-mentioned ranges of values relating to said reinforcing fillers, a person skilled in the art will still be able to adapt the amounts of other usual constituents, such as vulcanizing agents or else cobalt derivatives, or adapt the mixing processes to obtain the aforementioned values of modulus of elasticity and of tan (δ) _max .

According to an alternative embodiment of the invention, the tire comprising a layer C of rubber mixture arranged between at least the ends of said at least two working crown layers and said at least two crown layers. work having unequal axial widths, the distance d between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the rubber compound layer C is such that 1.1ø <d <2.2ø, ø being the diameter of the reinforcing elements of said at least one layer of circumferential reinforcing elements and, in a meridian plane, the thickness of the layer C of rubber mixture being substantially constant over the axial width between the axially inner end of the layer C and the end of the axially narrowest working layer.

For the purposes of the invention, the distance d is measured in a meridian plane from cable to cable, that is to say between the cable of a first working layer and the cable of a second working layer, according to a direction substantially perpendicular to the surfaces of the layer C. In other words, this distance d includes the thickness of the first layer C and the respective thicknesses of the calendering rubber mixtures, radially outside the cables of the radially inner working layer and radially inner to the cables of the radially outer working layer.

For the purposes of the invention, the thickness of the layer C of rubber mixture is measured between the two surfaces of said layer C according to the orthogonal projection of a point on one surface on the other surface.

For the purposes of the invention, the thickness of the layer C of rubber mixture is substantially constant, meaning that it does not vary by more than 0.3 mm. These variations in thickness are due only to creep phenomena during the manufacture and curing of the tire. Layer C in the form of a semi-finished, that is to say as elements ready to be used for producing a tire, thus advantageously has a constant thickness.

The various thickness measurements are taken on a cross section of a tire, the tire therefore being in an uninflated state.

The layer C of rubber mixture makes it possible to obtain a decoupling of said working crown layers in order to distribute the shear stresses over a greater thickness.

For the purposes of the invention, coupled layers are layers in which the respective reinforcing elements are radially separated by at most 1.5 mm, said thickness of rubber being measured radially between the upper and lower generatrices of said reinforcing elements, respectively.

The more usual tire designs provide for layers of rubber mix arranged between the ends of the working crown layers with greater thicknesses, in particular at the end of the narrowest working layer and with a thickness profile. non-homogeneous when the latter is viewed along a meridian section of the tire to allow such a thickness and to avoid too much disturbance to the environment of the end of the narrowest working layer. As explained above, the presence of this layer of rubber mixture makes it possible in particular to limit the shear stresses between the ends of the working crown layers, the circumferential rigidities of said working crown layers being zero at their end. The distance between the end of the axially narrowest working layer and the working layer separated from the axially narrowest working layer by the rubber compound layer, measured according to the definition of d above, is usually greater than 3.3 mm. This corresponds to a thickness of the rubber mixture layer of at least 2.5 mm while, generally, its thickness tends at each of its ends to a value less than 0.5 mm.

The inventors have been able to demonstrate that the presence of at least one layer of circumferential reinforcing elements makes it possible to maintain performance, in particular in terms of satisfactory endurance, with a layer C of rubber mixture of substantially constant thickness over the axial width. between the axially inner end of the layer C and the end of the axially narrowest working layer and such that the distance d is between 1.1ø and 2.2ø. It seems in fact that the presence of the layer of circumferential reinforcing elements contributes sufficiently to the absorption of at least part of the circumferential tension, in particular when passing through the contact area to reduce the shear stresses between the ends of the top layers of work.

The geometry of the layer C of rubber mixture in accordance with the invention also seems to go in the direction of better control of the flow of the mixtures during the manufacture of the tire and in particular during the curing of the latter.

Furthermore, the layer C of rubber mixture is thus advantageously in the semi-finished state in the form of a layer of constant thickness which is simple to manufacture and furthermore which can be stored simply. In fact, the layers usually used as described above which have a shape in section with variations in thickness are on the one hand more difficult to produce and on the other hand more difficult to store. In fact, variations in thickness create storage problems, these semi-finished products being most often stored in the form of winding on a reel. Layer C according to the invention is in the form of a semi-finished product with a section having a substantially flat profile compared to the layers usually used which are in the form of a semi-finished product with a section having a profile that is substantially round.

The manufacture and storage of the layer of rubber mixture in accordance with the invention in semi-finished form thus being so simplified, this may result in lower costs for the manufacture of the tire.

According to an advantageous embodiment of the invention, the axially widest working crown layer is radially inside the other working crown layers.

avec φ2, diamètre des éléments de renforcement de la couche de sommet de travail axialement la moins large. Une telle relation définit une zone d'engagement entre la couche de mélange caoutchouteux C et la couche de sommet de travail axialement la moins large. Un tel engagement en dessous d'une valeur égale à trois fois le diamètre des éléments de renforcement de la couche de travail axialement la moins large peut ne pas être suffisant pour obtenir un découplage des couche de sommet de travail pour notamment obtenir une atténuation des sollicitations en extrémité de la couche de sommet de travail axialement la moins large. Une valeur de cet engagement supérieure à vingt fois le diamètre des éléments de renforcement de la couche de travail axialement la moins large peut conduire à une diminution trop importante de la rigidité de dérive de l'armature de sommet du pneumatique.More preferably, the axial width D of the layer of rubber mix C between the axially innermost end of said layer of rubber mix C and the end of the axially narrowest working crown layer is such as : $$3.{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\varphi </figure-callout>}}_2\le \mathrm{D}\le 25.{\mathrm{<figure-callout\; id="2"\; label="\phi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\varphi </figure-callout>}}_2$$

with φ2, diameter of the reinforcing elements of the axially smallest working crown layer. Such a relationship defines an area of engagement between the rubber compound layer C and the axially narrower working crown layer. Such engagement below a value equal to three times the diameter of the reinforcing elements of the axially narrowest working layer may not be sufficient. to obtain a decoupling of the working crown layers in order in particular to obtain an attenuation of the stresses at the end of the axially narrower working crown layer. A value of this engagement greater than twenty times the diameter of the reinforcing elements of the axially smallest working layer can lead to an excessive reduction in the drift rigidity of the crown reinforcement of the tire.

Preferably, the axial width D of the layer of rubber mix C between the axially innermost end of said layer of rubber mix C and the end of the axially narrower working crown layer is greater. to 5 mm.

According to an advantageous variant embodiment of the invention, the layer of circumferential reinforcing elements has an axial width greater than 0.5 × W.

W is the maximum axial width of the tire, when the latter is mounted on its service rim and inflated to its recommended pressure.

The axial widths of the layers of reinforcing elements are measured on a cross section of a tire, the tire therefore being in an uninflated state.

According to a preferred embodiment of the invention, at least two working crown layers have different axial widths, the difference between the axial width of the axially widest working crown layer and the axial width of the crown layer. axially the narrowest work being between 10 and 30 mm.

According to a preferred embodiment of the invention, a layer of circumferential reinforcing elements is radially disposed between two working crown layers.

According to this embodiment of the invention, the layer of circumferential reinforcing elements makes it possible to limit more significantly the compressions of the reinforcing elements of the carcass reinforcement than a similar layer placed radially at the edge. outside of the working layers. She is preferably radially separated from the carcass reinforcement by at least one working layer so as to limit the stresses on said reinforcing elements and not to tire them too much.

Still advantageously according to the invention, the axial widths of the working crown layers radially adjacent to the layer of circumferential reinforcing elements are greater than the axial width of said layer of circumferential reinforcing elements and preferably said crown layers working elements adjacent to the layer of circumferential reinforcing elements are on either side of the equatorial plane and in the immediate axial extension of the layer of circumferential reinforcing elements coupled over an axial width, to be then decoupled by a layer C of rubber mixture at least over the remainder of the width common to said two working layers.

The presence of such couplings between the working crown layers adjacent to the layer of circumferential reinforcement elements allows the reduction of the tensile stresses acting on the circumferential elements axially outermost and located closest to the coupling.

According to an advantageous embodiment of the invention, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus less than 150 GPa.

According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 100 GPa and greater than 20 GPa, preferably between 30 and 90 GPa and more preferably still below 80 GPa.

Also preferably, the maximum tangent modulus of the reinforcing elements is less than 130 GPa and more preferably still less than 120 GPa.

The moduli expressed above are measured on a tensile stress curve as a function of the elongation determined with a prestress of 20 MPa reduced to the metal section of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the metal section of the reinforcing element.

The moduli of the same reinforcing elements can be measured on a tensile stress curve as a function of the elongation determined with a prestress of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element. The overall cross section of the reinforcing element is the cross section of a composite element made of metal and rubber, the latter having in particular penetrated the reinforcing element during the tire curing phase.

According to this formulation relating to the overall section of the reinforcing element, the reinforcing elements of the axially outer parts and of the central part of at least one layer of circumferential reinforcing elements are metal reinforcing elements having a secant modulus. at 0.7% elongation between 5 and 60 GPa and a maximum tangent modulus less than 75 GPa.

According to a preferred embodiment, the secant modulus of the reinforcing elements at 0.7% elongation is less than 50 GPa and greater than 10 GPa, preferably between 15 and 45 GPa and more preferably still below 40 GPa.

Also preferably, the maximum tangent modulus of the reinforcing elements is less than 65 GPa and more preferably still less than 60 GPa.

According to a preferred embodiment, the reinforcing elements of at least one layer of circumferential reinforcing elements are metallic reinforcing elements exhibiting a tensile stress curve as a function of the relative elongation, having low slopes for low elongations. and a substantially constant and steep slope for higher elongations. Such reinforcing elements for the additional ply are usually referred to as “bi-modulus” elements.

According to a preferred embodiment of the invention, the substantially constant and steep slope appears from a relative elongation of between 0.1% and 0.5%.

The various characteristics of the reinforcing elements stated above are measured on reinforcing elements taken from tires.

Reinforcing elements more particularly suited to the production of at least one layer of circumferential reinforcing elements according to the invention are for example assemblies of formula 21.23, the construction of which is 3x (0.26 + 6x0.23) 4.4 / 6.6 SS; this stranded cable consists of 21 elementary wires of formula 3 x (1 + 6), with 3 strands twisted together each consisting of 7 wires, one wire forming a central core with a diameter equal to 26/100 mm and 6 wires wound diameter equal to 23/100 mm. Such a cable has a secant modulus at 0.7% equal to 45 GPa and a maximum tangent modulus equal to 98 GPa, measured on a tensile stress curve as a function of the elongation determined with a prestress of 20 MPa reduced to the section. of metal of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a preload of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension reduced to the overall section of the reinforcing element. reinforcement, this cable of formula 21.23 has a secant modulus at 0.7% equal to 23 GPa and a maximum tangent modulus equal to 49 GPa.

Likewise, another example of reinforcing elements is an assembly of formula 21.28, whose construction is 3x (0.32 + 6x0.28) 6.2 / 9.3 SS. This cable has a secant modulus at 0.7% equal to 56 GPa and a maximum tangent modulus equal to 102 GPa, measured on a tensile stress curve as a function of the elongation determined with a prestress of 20 MPa reduced to the section of metal of the reinforcing element, the tensile stress corresponding to a measured tension brought back to the metal section of the reinforcing element. On a tensile stress curve as a function of the elongation determined with a pre-stress of 10 MPa reduced to the overall section of the reinforcing element, the tensile stress corresponding to a measured tension reduced to the overall section of the element of reinforcement, this cable of formula 21.28 has a secant modulus at 0.7% equal to 27 GPa and a maximum tangent modulus equal to 49 GPa.

The use of such reinforcing elements in at least one layer of circumferential reinforcing elements makes it possible in particular to maintain satisfactory rigidities of the layer, including after the shaping and curing steps in usual manufacturing processes.

According to a second embodiment of the invention, the circumferential reinforcement elements can be formed from inextensible metal elements and cut so as to form sections of length much less than the circumference of the shortest layer, but preferably greater than 0.1 times said circumference, the cuts between sections being axially offset with respect to each other. More preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working crown layer. Such an embodiment makes it possible to confer, in a simple manner, on the layer of circumferential reinforcing elements a modulus which can easily be adjusted (by the choice of the intervals between sections of the same row), but in all cases lower. than the modulus of the layer made up of the same metallic elements but continuous, the modulus of the additional layer being measured on a vulcanized layer of cut elements, taken from the tire.

According to a third embodiment of the invention, the circumferential reinforcement elements are corrugated metal elements, the a / λ ratio of the ripple amplitude over the wavelength being at most equal to 0.09. Preferably, the tensile modulus of elasticity per unit width of the additional layer is less than the tensile modulus of elasticity, measured under the same conditions, of the most extensible working crown layer.

The metallic elements are preferably steel cables.

According to a preferred embodiment of the invention, the reinforcing elements of the working crown layers are inextensible metal cables.

Advantageously according to the invention, the crown reinforcement is formed from at least two working crown layers of reinforcing elements, crossed with a layer to the other by making angles between 10 ° and 45 ° with the circumferential direction.

The invention further advantageously provides, in order to reduce the tension stresses acting on the axially outermost circumferential elements, that the angle formed with the circumferential direction by the reinforcing elements of the working crown layers is less than 30 ° and preferably less than 25 °.

According to another advantageous variant of the invention, the working crown layers comprise reinforcing elements, crossed from one ply to the other, forming with the circumferential direction varying angles in the axial direction, said angles being greater than the axially outer edges of the layers of reinforcing elements with respect to the angles of said elements measured at the level of the circumferential mid-plane. Such an embodiment of the invention makes it possible to increase the circumferential rigidity in certain zones and, on the contrary, to reduce it in others, in particular to reduce the compression of the carcass reinforcement.

A preferred embodiment of the invention also provides that the crown reinforcement is completed radially on the outside by at least one additional layer, called protective, of so-called elastic reinforcing elements, oriented relative to the circumferential direction with a angle between 10 ° and 45 ° and in the same direction as the angle formed by the inextensible elements of the working layer which is radially adjacent to it.

The protective layer may have an axial width less than the axial width of the narrowest working layer. Said protective layer may also have an axial width greater than the axial width of the narrower working layer, such as to cover the edges of the narrower working layer and, in the case of the radially upper layer as being the narrowest, as it is coupled, in the axial extension of the additional reinforcement, with the widest working crown layer over an axial width, in order to then be, axially on the outside, decoupled from said widest working layer by profiles with a thickness of at least 2 mm. The protective layer formed of elastic reinforcing elements can, in the case mentioned above, on the one hand possibly be decoupled from the edges of said working layer. less wide by profiles of thickness substantially less than the thickness of the profiles separating the edges of the two working layers, and on the other hand have an axial width less than or greater than the axial width of the widest crown layer.

According to any one of the embodiments of the invention mentioned above, the crown reinforcement can still be completed, radially on the inside between the carcass reinforcement and the radially inner working layer closest to said reinforcement carcass, by a triangulation layer of inextensible metallic steel reinforcement elements forming, with the circumferential direction, an angle greater than 45 ° and in the same direction as that of the angle formed by the radially reinforcing elements of the layer closest to the carcass reinforcement.

• figure 1, une vue méridienne d'un schéma d'un pneumatique selon l'invention,
• figure 2, une vue en projection d'un schéma d'une partie de la surface d'une bande de roulement d'un pneumatique selon l'invention,
• figure 3, une vue en coupe selon le plan P₁ d'une découpure longitudinale selon un mode de réalisation de l'invention,
• figure 4, une vue en coupe selon le plan P₂ d'une découpure transversale selon un mode de réalisation de l'invention.

Other details and advantageous characteristics of the invention will emerge below from the description of the embodiments of the invention with reference to figures 1 to 4 that represent :

• figure 1 , a meridian view of a diagram of a tire according to the invention,
• figure 2 , a projection view of a diagram of part of the surface of a tread of a tire according to the invention,
• figure 3 , a sectional view along the plane P ₁ of a longitudinal cutout according to one embodiment of the invention,
• figure 4 , a sectional view along the plane P ₂ of a transverse cutout according to one embodiment of the invention.

The figures are not shown to scale for ease of understanding. The figure 1 shows only a half-view of a tire which is extended symmetrically with respect to the axis XX 'which represents the circumferential median plane, or equatorial plane, of a tire.

• d'une première couche de travail 41 formée de câbles métalliques inextensibles 9.28 non frettés, continus sur toute la largeur de la nappe, orientés d'un angle égal à 24°,
• d'une couche d'éléments de renforcement circonférentiels 42 formée de câbles métalliques en acier 21x23, de type "bi-module",
• d'une seconde couche de travail 43 formée de câbles métalliques inextensibles 9.28 non frettés, continus sur toute la largeur de la nappe, orientés d'un angle égal à 24° et croisés avec les câbles métalliques de la couche 41,
• d'une couche de protection 44 formées de câbles métalliques élastiques 6.35.

On the figure 1 , the tire 1, of dimension 315/70 R 22.5, has an aspect ratio H / S equal to 0.70, H being the height of the tire 1 on its mounting rim and S its maximum axial width. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads, not shown in the figure. The carcass reinforcement is formed from a single layer of metal cables. This carcass reinforcement 2 is shrunk by a crown reinforcement 4, formed radially from the inside to the outside:

• a first working layer 41 formed of non-wrapped inextensible metal cables 9.28, continuous over the entire width of the ply, oriented at an angle equal to 24 °,
• a layer of circumferential reinforcing elements 42 formed of 21x23 steel metal cables, of the "bi-modulus" type,
• a second working layer 43 formed of non-wrapped inextensible metal cables 9.28, continuous over the entire width of the ply, oriented at an angle equal to 24 ° and crossed with the metal cables of layer 41,
• a protective layer 44 formed of elastic metal cables 6.35.

The crown frame is itself capped with a tread 6.

The maximum axial width W of the tire is equal to 317 mm.

The axial width L ₄₁ of the first working layer 41 is equal to 252 mm.

The axial width L ₄₃ of the second working layer 43 is equal to 232 mm.

As for the axial width L ₄₂ of the layer of circumferential reinforcing elements 42, it is equal to 194 mm.

The last crown ply 44, called protection, has a width L ₄₄ equal to 124 mm.

According to the invention, the modulus of elasticity under tension at 10% elongation of the calendering layers of each of the working layers 41 and 43 is equal to 10.03 MPa.

The figure 2 illustrates a projection view of a diagram of part of the surface 6 of a tread 5 of a tire 1. The surface 6 of the tread 5 is formed of longitudinal cutouts 7 and 8, and of transverse cutouts 9 and 10. The longitudinal 7 and transverse 9 cutouts are grooves and the cutouts longitudinal 8 and transverse 10 are incisions. All of these cutouts 7, 8, 9 and 10 form the tread elements 11 constituting the tread 5.

On the figure 3 , is schematically shown a longitudinal cutout 8 in section along the section plane P ₁ . This section plane P ₁ is perpendicular to the mean plane of the walls and to the plane tangent to the surface 6 of the tread 5. The width D _f of the cutout 8 at the bottom of the cutout is equal to 6 mm. The width d _s of the longitudinal cutout 8 at the surface of the tread 5 is measured between the ends 12 and 13 of said longitudinal cutout 8 at the surface 6 of the tread 5. It is equal to 0.7 mm. The ratio D _f / d _s is equal to 8.57.

On the figure 4 , is schematically shown a transverse cutout 10 in section along the section plane P ₂ . This section plane P ₂ is perpendicular to the mean plane of the walls and to the plane tangent to the surface 6 of the tread 5. The width D _f 'of the transverse cutout 10 at the bottom of the cutout is equal to 7 mm. The width d _s ' of the transverse cutout 10 of the tread 5 is measured between the ends 14 and 15 of said transverse cutout 10 at the surface 6 of the tread 5. It is equal to 0.7 mm. The ratio D _f '/ d _s ' is equal to 10.

In the case of figures 3 and 4 , the cutouts 8 and 10 form an incision in the surface of the tread which, in accordance with the definition given above, has a width of less than 2 mm. After wear of the tread, the hollow hidden under said incision reveals a groove. As explained above, when the tire is new, the incision makes it possible to form ridges while maintaining a high degree of rigidity of the tread, the walls coming into contact with one another at the time of contact with the ground. After wear, when the hidden hollow appears, it forms a groove and therefore ridges, the loss of rigidity being limited due to the lesser depth of the cutout in the tread.

Tests were carried out with various tires produced according to the invention and compared with reference tires.

Tests are carried out in particular by varying the characteristics of the mixtures of the calendering of the working layers 41 and 43, in particular the value tan (δ) _max .

The different mixtures used are listed below. Mixture R1 Mixture 1 NR 100 100 Black N347 52 Black N683 63 Antioxidant (6PPD) 1 1 Stearic acid 0.65 0.65 Zinc oxide 9.3 9.3 Cobalt Salt (AcacCo) 1.12 1.12 sulfur 6.1 6.1 DCBS accelerator 0.93 0.93 PTC retarder (PVI) 0.25 0.25 MA ₁₀ (MPa) 10.4 10.03 tan (δ) _max 0.130 0.092 P60 (%) 22.9 17.4

The tires 1 according to the invention are produced in accordance with figures 1 to 4 and they have working layers whose calenders consist of mixture 1.

The first reference tires T ₁ are produced in accordance with figures 2-4 , they have working layers the calenders of which consist of mixture 1 and their crown architecture differs in that the crown reinforcement does not include a layer of circumferential reinforcing elements.

Second reference tires T ₂ are produced in accordance with figures 1-4 and they have working layers whose calenders consist of the mixture R1.

The first tests consisted of running simulating average use of the tires when fitted to heavy-duty vehicles. The purpose of these tests is to check the condition of the tires during travel and to identify any problems of irregular wear of the tread.

During travel, the reference tires T ₁ show wear irregularities in the circumferential direction. Such wear irregularities can under certain conditions have negative effects on the grip properties of the tire because the surface of the contact patch can be modified. In addition, the appearance of such wear irregularities leads to an increase in the rate of wear of the tires and therefore a shorter period of use than expected.

Concerning the tires according to the invention and the reference tires T ₂ , the tests show that such wear irregularities appear later and in a much less pronounced manner so that the grip properties are hardly affected whatever the driving conditions.

Second tests corresponding to endurance tests were carried out on a test machine requiring each of the tires to run in a straight line at a speed equal to the maximum speed index prescribed for said tire (speed index) under an initial load. of 4000 Kg gradually increased to reduce the duration of the test.

It turns out that all of the tires tested show substantially comparable results.

A third type of tests also corresponding to endurance tests were carried out on a test machine cyclically imposing a transverse force and a dynamic overload on the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires.

The distances traveled vary from one type of tire to another, with losses appearing due to a degradation of the rubber compounds at of the ends of the working layers. The results are expressed in the following table with reference to a base 100 fixed for the reference tire T ₁ . T ₁ tire T ₂ tire Pneumatic I 100 105 105

These tests show in particular that the design of the tires according to the invention allows the use of mixtures of calendering of the working crown layers exhibiting less favorable cohesion without adversely affecting endurance performance when a layer of circumferential reinforcing elements is present.

In addition, rolling resistance measurements were taken. These measurements were carried out on the reference tire T2 as described above, and on tires according to the invention I as described above, the mixture 1 being used for the calendering layers of the working layers 41 and 43.

The results of the measurements are presented in the following table; they are expressed in Kg / t, a value of 100 being assigned to the tire T ₂ . T ₂ tire Pneumatic I 100 98

Claims (13)

1. Tyre (1) having a radial carcass reinforcement (2) comprising a crown reinforcement (4) formed of at least two working crown layers of reinforcing elements (41, 43), each formed of reinforcing elements inserted between two calendering layers of rubber compound, itself capped radially with a tread (5), said tread being joined to two beads via two sidewalls, the crown reinforcement (4) comprising at least one layer of circumferential reinforcing elements (42), the tensile elastic modulus at 10% elongation of at least one calendering layer of at least one working crown layer (41, 43) being greater than 9 MPa, the measurement of said modulus being performed under tension according to standard AFNOR-NFT-46002 of September 1988 in normal temperature and relative humidity conditions according to standard AFNOR-NFT-40101 of December 1979 and the maximum value of tan(δ), denoted tan(δ)max, of said at least one calendering layer of at least one working crown layer (41, 43) being less than 0.100, the measurement of tan(δ) being performed according to Standard ASTM D 5992-96, said tread comprising a tread surface (6) intended to come into contact with a road surface and form a contact surface, characterized in that said tread consists of at least one central part extending at least in the region of the equatorial plane and two axially exterior parts and has, at least in said central part, at least one longitudinally-oriented cut (8) and at least one transversely-oriented cut (10), a longitudinally-oriented cut being a cut in which the mean plane of at least a portion of the walls of said at least one cut forms an angle with a longitudinal plane of less than 10°, a transversely-oriented cut being a cut in which the mean plane of at least a portion of the walls of said at least one cut forms an angle with a radial plane of less than 35°, in that the depth, measured on a new tyre in at least said central part, of said at least one longitudinally-oriented cut (8) is greater than or equal to 40% of the thickness of the tread, in that the ratio of the width (D_f) measured at the bottom of said at least one longitudinally-oriented cut (8) to the width (d_S) measured at the surface of the tread on a new tyre of said at least one longitudinally-oriented cut (8) is greater than 1.2, in that the depth, measured on a new tyre in at least said central part, of said at least one transversely-oriented cut (10) is greater than or equal to 40% of the thickness of the tread, and in that the ratio of the width (D'_f) measured at the bottom of said at least one transversely-oriented cut (10) to the width (d'_S) measured at the surface of the tread on a new tyre of said at least one transversely-oriented cut (10) is greater than or equal to 1.
2. Tyre (1) according to Claim 1, characterized in that the ratio of the width (D'_f) measured at the bottom of said at least one transversely-oriented cut (10) to the width (d'_S) measured at the surface of the tread on a new tyre of said at least one transversely-oriented cut (10) is greater than 1.2.
3. Tyre (1) according to Claim 1 or 2, characterized in that the width (D'_f) measured at the bottom of said at least one transversely-oriented cut (10) is strictly greater than 2 mm.
4. Tyre (1) according to Claim 3, characterized in that the width (D'_f) measured at the bottom of said at least one transversely-oriented cut (10) is preferably less than 10 mm.
5. Tyre (1) according to Claims 1 to 4, characterized in that the width (D_f) measured at the bottom of said at least one longitudinally-oriented cut (8) is strictly greater than 3 mm.
6. Tyre (1) according to Claim 5, characterized in that the width (D_f) measured at the bottom of said at least one longitudinally-oriented cut (8) is less than 10 mm.
7. Tyre (1) according to one of the preceding claims, characterized in that said at least one calendering layer of at least one working crown layer (41, 43) is an elastomer compound based on natural rubber or on synthetic polyisoprene with a predominance of cis-1,4- linkages and optionally at least one other diene elastomer, the natural rubber or synthetic polyisoprene in the case of a blend being present at a predominant content relative to the content of the other diene elastomer(s) used, and on a reinforcing filler composed:

   a) either of carbon black with a BET specific surface area of less than 60 m²/g regardless of its oil absorption number, used at a content of between 40 and 100 phr and preferably of between 60 and 90 phr,

   b) or of a white filler of the silica and/or alumina type comprising SiOH and/or AlOH surface functions selected from the group formed of precipitated or fumed silicas, aluminas or aluminosilicates or else carbon blacks modified during or after synthesis with a BET specific surface area of between 30 and 260 m²/g used at a content of between 40 and 100 phr and preferably between 60 and 90 phr,

   c) or of a blend of carbon black described in (a) and a white filler described in (b), wherein the overall filler content is between 40 and 100 phr, and preferably between 60 and 90 phr,

   the BET specific surface area measurement being performed in accordance with the Brunauer, Emmet and Teller method described in "The Journal of the American Chemical Society», vol. 60, page 309, February 1938, corresponding to the standard NFT 45007 of November 1987.
8. Tyre (1) according to one of the preceding claims, a layer C of rubber compound being arranged between at least the ends of said at least two working crown layers (41, 43) and said at least two working crown layers (41, 43) having unequal axial widths, characterized in that the distance d between the end of the axially narrowest working layer (43) and the working layer (41) separated from the axially narrowest working layer (43) by the layer C of rubber compound is such that 1.1ø < d < 2.2ø, ø being the diameter of the reinforcing elements of said at least one layer of circumferential reinforcing elements and in that, in a meridian plane, the thickness of the layer C of rubber compound is substantially constant over the axial width between the axially interior end of the layer C of rubber compound and the end of the axially narrowest working layer (43).
9. Tyre (1) according to one of the preceding claims, characterized in that the layer of circumferential reinforcing elements (42) is radially arranged between two working crown layers (41, 43).
10. Tyre (1) according to one of the preceding claims, characterized in that the crown reinforcement (4) is formed of at least two working crown layers of reinforcing elements (41, 43), preferably inextensible, crossed from one layer to the other, forming, with the circumferential direction, angles of between 10° and 45°.
11. Tyre (1) according to one of the preceding claims, characterized in that the reinforcing elements of at least one layer of circumferential reinforcing elements (42) are metal reinforcing elements having a secant modulus at 0.7% elongation of between 10 and 120 GPa and a maximum tangent modulus of less than 150 GPa, the measurements of secant modulus and tangent modulus being performed under tension according to standard ISO 6892 of 1984.
12. Tyre (1) according to one of the preceding claims, characterized in that the crown reinforcement (4) is supplemented radially on the outside by at least one additional ply (44), referred to as a protective ply, of reinforcing elements, referred to as elastic reinforcing elements, that are oriented relative to the circumferential direction at an angle of between 10° and 45° and in the same direction as the angle formed by the inextensible elements of the working ply (43) which is radially adjacent thereto.
13. Tyre (1) according to one of the preceding claims, characterized in that the crown reinforcement (4) also comprises a triangulation layer formed of metal reinforcing elements that form angles of more than 45° with the circumferential direction.

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